CTENOPHOR^E I BEROIDjE. 509 



equal in length the diameter of the sphere, or surpass it, 

 and increase to two, three, five, ten, and twenty times 

 the diameter of the body, and more and more ; so much 

 so, that it would seem as if these threads had the power 

 of endless extension and development. But, as they 

 lengthen, they appear more complicated : from one of 

 their sides other delicate threads shoot out like fringes, 

 forming a row of beards like those of the most elegant 

 ostrich feather, and each of these threads itself elongates 

 till it equals in .length the diameter of the whole body, 

 and bends in the most graceful curves." 



BEROID.E. This Family contains Beroe, Idyia, and 

 their allies. 



The Genus Idyia contains /. roseola, Ag., of the coast 

 of New England and northward. This species attains 

 the length of three or four inches or more, and is of a 

 beautiful rose-color. It sometimes appears in such num- 

 bers during the summer months as to tinge large patches 

 of the sea with a delicate rosy hue. It is very voracious, 

 and feeds chiefly on other ctenophorae. 



SUB-SECTION II. 



THE ORDER OF DISCOPHORAE, OR MEDUSA PROPER. 



THE Discophorae comprise jelly-fishes which have the 

 form of a hemispheric disk spreading uniformly in all di- 

 rections. They abound in all seas, and the species are 

 numerous. Agassiz recognizes three sub-orders, fifteen 

 families, and about seventy genera. 



The Sub-Order Rhizostomeae includes those discophorae 

 which are generally regarded as destitute of the so-called 

 mouth, and which absorb their food through innumerable 

 tubes traversing the arms, and reaching the digestive 

 cavity through narrow channels ; and they are wholly 

 destitute of marginal tentacles. As to the mouth, how- 

 ever, Agassiz holds, if we understand him rightly, that 



